The invention relates to the field of seal joints of nuclear reactor instrument penetrations. More particularly, the invention is a method of repairing a leaky seal joint between a pressure stub tube and a thermocouple concentrically mounted in the tube by means of a compression fitting.
Prior art seal joint structures for instrument penetration of reactor pressure barriers involve compression fittings having fitting bodies and nuts threaded thereon which radially cam swaging ferrules to clinch and seal an outer pressure stub tube and a thermocouple having a smaller outside diameter cylindrical surface than the inside diameter of the tube to provide a seal joint for the penetration. Typically, the penetration is through the reactor head and, in use, there is exposure of the sealed and jointed parts to elevated temperature, pressure and nuclear radiation. The fittings may, typically, be of the ferrule containing type sold under the trademark "Swagelok" by Crawford Fitting Company of Cleveland, Ohio, or sold under the trademark "Tylok" by Tylok International of Cleveland, Ohio.
The reactor head members of at least one manufacturer of nuclear reactor units, generally, have between 39 and 65 penetrations with compression seal joints. Leaky seal joints often cause contaminated water to spill onto the head area, contaminating this zone and complicating worker access thereto, thereby increasing worker rems or exposure to radiation time.